Reading between the vines: Hosts as islands for extreme holoparasitic plants.

PREMISE OF THE STUDY: Partitioning of population genetic variation in plants may be affected by numerous factors including life history and dispersal characteristics. In parasitic plants, interactions with host populations may be an additional factor influencing partitioning. To test for hierarchical population genetic patterns related to obligate endoparasitism, we studied three species of Rafflesiaceae, which grow as extremely reduced endophytes infecting Tetrastigma vines in Southeast Asia. METHODS: Microsatellite markers were developed and multilocus genotypes were determined for Rafflesia cantleyi, Rafflesia tuan-mudae, and Sapria himalayana and each of their Tetrastigma hosts. Relatedness among parasite individuals was estimated, and AMOVAs were used to determine levels of population genetic subdivision. KEY RESULTS: Microsatellite genotypes for 340 paired parasite and host samples revealed that host vines were infected by numerous Rafflesiaceae individuals that may spread for up to 14 m within stem tissues. Surprisingly, Rafflesiaceae parasites within a given host are significantly more closely related to each other than individuals of the same species in other host individuals. The pattern of hierarchical population genetic subdivision we detected across species is likely due to limited seed dispersal with reinfection of natal host vines. CONCLUSIONS: These findings demonstrate common population genetic patterns between animal and plant parasites, potentially indicating advantages of close relatives infecting hosts. This study also has important conservation implications for Rafflesiaceae since our data suggest that destruction of a single infected host vine could result in large genetic losses.

Increased phylogenetic resolution within the ecologically important Rhizopogon subgenus Amylopogon using 10 anonymous nuclear loci.

Rhizopogon species are ecologically significant ectomycorrhizal fungi in conifer ecosystems. The importance of this system merits the development and utilization of a more robust set of molecular markers specifically designed to evaluate their evolutionary ecology. Anonymous nuclear loci (ANL) were developed for R. subgenus Amylopogon. Members of this subgenus occur throughout the United States and are exclusive fungal symbionts associated with Pterospora andromedea, a threatened mycoheterotrophic plant endemic to disjunct eastern and western regions of North America. Candidate ANL were developed from 454 shotgun pyrosequencing and assessed for positive amplification across targeted species, sequencing success, and recovery of phylogenetically informative sites. Ten ANL were successfully developed and were subsequently used to sequence representative taxa, herbaria holotype and paratype specimens in R. subgenus Amylopogon. Phylogenetic reconstructions were performed on individual and concatenated data sets by Bayesian inference and maximum likelihood methods. Phylogenetic analyses of these 10 ANL were compared with a phylogeny traditionally constructed using the universal fungal barcode nuc rDNA ITS1-5.8S-ITS2 region (ITS). The resulting ANL phylogeny was consistent with most of the species designations delineated by ITS. However, the ANL phylogeny provided much greater phylogenetic resolution, yielding new evidence for cryptic species within previously defined species of R. subgenus Amylopogon. Additionally, the rooted ANL phylogeny provided an alternate topology to the ITS phylogeny, which inferred a novel set of evolutionary relationships not identified in prior phylogenetic studies.

Development of microsatellite markers for the medicinal plant Isodon rubescens (Lamiaceae) and related species.

PREMISE OF THE STUDY: Microsatellite markers were developed for the medicinal plant Isodon rubescens to investigate genetic variability of the species and, in future studies, to assess its relation to the content of pharmacologically active chemicals produced by the plant. METHODS AND RESULTS: Eleven primer pairs were identified and tested in multiple populations of I. rubescens and related species (I. henryi, I. enanderianus, I. lophanthoides) from the People's Republic of China. The primers amplified dinucleotide repeats and had between two and 12 alleles per locus in a given population. CONCLUSIONS: These microsatellites will be useful for understanding patterns of phytochemical variation in I. rubescens and have the potential to be applied to research on evolutionary processes in other species of the genus Isodon.

Microsatellite marker development for the coastal dune shrub Prunus maritima (Rosaceae).

UNLABELLED: • PREMISE OF THE STUDY: Microsatellite primers were developed in the beach plum, Prunus maritima, to investigate the genetic composition of remaining populations in need of conservation and, in future studies, to determine its relation to P. maritima var. gravesii. • METHODS AND RESULTS: Fourteen primer pairs were identified and tested in four populations throughout the species' geographic range. Of these 14 loci, 12 were shown to be polymorphic among a total of 60 P. maritima individuals sampled (15 individuals sampled from four populations). Among the polymorphic loci, the number of alleles ranged from two to 10 and observed heterozygosity of loci ranged from 0.07 to 0.93 among specimens tested. • CONCLUSIONS: These microsatellites will be useful in evaluating the population genetic composition of P. maritima and in developing approaches for further conservation and management of this species within the endangered coastal dune ecosystem of the northeastern United States.

Characterization of microsatellite markers for pinedrops, Pterospora andromedea (Ericaceae), from Illumina MiSeq sequencing.

PREMISE OF THE STUDY: Pterospora andromedea (Ericaceae) is a mycoheterotrophic plant endemic to North America with a disjunct distribution. Eastern populations are in decline compared to western populations. Microsatellite loci will allow comparison of genetic diversity in endangered to nonthreatened populations. • METHODS AND RESULTS: Illumina MiSeq sequencing resulted in development of 12 polymorphic microsatellite loci from 63 perfect microsatellite loci tested. One polymorphic locus was obtained from a traditional enrichment method. These 13 loci were screened across two western and two eastern populations. For western and eastern populations, respectively, number of alleles ranged from one to 10 and one to four, and observed heterozygosity ranged from 0.000 to 0.389 and 0.000 to 0.143. • CONCLUSIONS: These are the first microsatellite loci developed for Pterospora. They will be useful in conservation efforts of the eastern populations and for examination of population genetic parameters at different geographic scales and comparison with mycorrhizal fungal hosts.

Microsatellite primers for the fungi Rhizopogon kretzerae and R. salebrosus (Rhizopogonaceae) from 454 shotgun pyrosequencing.

PREMISE OF THE STUDY: Rhizopogon kretzerae and R. salebrosus (Rhizopogonaceae) are ectomycorrhizal fungi symbiotic with pines and the mycoheterotrophic plant Pterospora andromedea (Ericaceae). Microsatellite loci will allow population genetic study of fungal hosts to P. andromedea. • METHODS AND RESULTS: Shotgun pyrosequencing of R. kretzerae DNA resulted in primer development of 23 perfect microsatellite loci and screened across two populations each for R. kretzerae and R. salebrosus. Twelve loci were polymorphic in R. kretzerae populations, and 11 loci cross-amplified in R. salebrosus populations. For R. kretzerae and R. salebrosus, number of alleles was one to eight and one to nine, respectively, and observed heterozygosity ranged from 0.00-0.57 and 0.00-0.70, respectively. • CONCLUSIONS: These are the first microsatellite loci developed for any species within Rhizopogon subgenus Amylopogon. These microsatellite loci will be used in conservation genetic studies of rare to endangered eastern populations and to compare plant and fungal population genetic structure at different hierarchical levels.

An efficient technique for primer development and application that integrates fluorescent labeling and multiplex PCR.

PREMISE OF THE STUDY: Development of genetic markers can be costly and time-consuming, especially when multiple primer pairs are fluorescently labeled. This step was streamlined by combining two techniques in the same PCR reaction: (1) custom-labeling of primers by the investigator and (2) multiplexing multiple primers together in the same reaction. • METHODS AND RESULTS: This technique was successfully used to develop microsatellite markers in several plant species. Microsatellites amplified with this multiplexing process were identical to those generated from PCR using individual primer pairs and with traditional methods using a priori labeled fluorescent primers. Tests of PCR cycling programs revealed that conditions recommended for the commercial kit generated stronger fragment peaks than the previously recommended cycling protocol. • CONCLUSIONS: This technique is an efficient and economical way to fluorescently label multiple microsatellite primers in the same reaction. It is also applicable to other markers used in PCR amplification of genetic material.

Comparative analysis of the reproductive ecology of Monotropa and Monotropsis: Two mycoheterotrophic genera in the Monotropoideae (Ericaceae).

Studies of mycoheterotrophs, defined as plants that obtain carbon resources from associated mycorrhizal fungi, have fundamentally contributed to our understanding of the importance and complexity of symbiotic ecological interactions. However, to date, the reproductive ecology of these organisms remains empirically understudied, with existing literature presenting hypotheses about traits including a generalist pollination syndrome and autogamous self-pollination. To address this gap in our knowledge of the reproductive ecology of mycoheterotrophic plants, we comparatively analyzed three species of two monotropoid genera, Monotropa and Monotropsis. During three consecutive years of field observations and manipulations of four populations of Monotropa uniflora, seven of M. hypopitys (both red and yellow color forms), and two of Monotropsis odorata, we investigated flowering phenology, pollination ecology, breeding system, floral herbivory, and reproductive effort and output. Contrary to previous predictions, our results revealed that taxa are largely outcross-pollinated and specialized toward Bombus pollinators. Additionally, species differ in breeding system, timing and duration of reproductive development, fluctuations in reproductive effort and output, and fitness impacts of herbivory. This study is the first thorough investigation of the reproductive ecology of mycoheterotrophic species and provides insight into possible limitations in reproductive traits imposed by a mycoheterotrophic life history.

Cryptic bracts facilitate herbivore avoidance in the mycoheterotrophic plant Monotropsis odorata (Ericaceae).

Plant coloration, shown to play a dynamic role in animal attraction, has been proposed as a means of defense, although these reports lack experimental evidence. This study empirically assesses defensive coloration in the mycoheterotrophic plant, Monotropsis odorata, which produces stems and flowers covered by dried vegetative bracts. Field studies were conducted using an experimental group of plants with bracts removed and a control group to evaluate the frequency of and fitness impacts associated with herbivory. Additionally, we quantitatively assessed the reflectance spectra of bracts, stems, and flowers of M. odorata relative to an ambient leaf litter substrate. Across the 2-yr study, the experimental group experienced a 20-27% higher mean herbivory rate and 7-20% lower mean fruit production relative to the control group. Bracts were shown to strongly resemble ambient leaf litter in spectral analyses, with stems and flowers having more conspicuous coloration. Results show that the presence of dried bracts effectively camouflages conspicuous stem and floral tissues, significantly reducing the frequency of floral and stem herbivory, and thereby increasing fruit set, a component of plant fitness. This study supports the principal hypothesis that coloration can play a fundamental role in plant defense.